Dr Neal D Hulkower reviews Behind the Glass: The Chemical & Sensorial Terroir of Wine Tasting by Gus Zhu MW.
In the late 1960s and ’70s, when I first waded into the world of fine wine, I don’t recall there being any books or periodicals that offered a novice nontechnical descriptions of what creates the aromas and flavors in a wine and how our senses interpret them. And honestly, I wasn’t looking for any. I was content to explore wine purely hedonistically as a welcome respite from my very left-brained graduate studies. The last thing I was thinking about when sipping a claret or Spätlese was its chemical composition and which part of my tongue or nasal receptors were being stimulated.
But over the decades, familiarity bred curiosity—not just in me, but also in the folks I host in a tasting room at the top of the Dundee Hills in Oregon’s Willamette Valley. For example, I was recently asked about a Pinot Noir rosé, “What am I tasting?” I demurred. Falling back on what I had learned from Neuroenology: How the Brain Creates the Taste of Wine (Columbia University Press, 2016), by Yale neuroscience professor Gordon M Shepherd, and I Taste Red: The Science of Tasting Wine (University of California Press, 2016), by British wine writer, wine judge, and plant biologist Dr Jamie Goode, I pointed out that there was no way I could perceive what the questioner was tasting. Each of the authors has the scientific chops to steer us through the paths that our senses go through to create the flavors we detect. Goode’s significantly greater experience in the wine world gives him the edge in offering practical advice to the taster.
There is now a new source from which to learn more about what makes wine so enticing. Behind the Glass: The Chemical & Sensorial Terroir of Wine Tasting by Gus Zhu MW is the latest to offer insights to the neophyte enophile, addressing questions in a less technical way than Shepherd and Goode. (Gus) Jian Zhu is well qualified to take on the task of guiding the reader through the complex (and still not completely understood) web of interactions one experiences when tasting. In addition to becoming the first Chinese Master of Wine in 2019, Zhu is coauthor of a review paper entitled “A Quarter Century of Wine Pigment Discovery,” which appeared the same year in the Journal of the Science of Food and Agriculture, and he is a research and development scientist at Cork Supply and Tonnellerie Ô, both in Benicia, California, south of Napa Valley. He lists as specialties wine pigments and sensory evaluation. Each plays a major role in his exposition.
Related
In the introduction, Zhu’s motivation for writing the book is revealed: “I have often been asked to explain the science behind why a glass of wine tastes the way it does.” It boils down to the complex chemistry, which is understood to some degree, and to our senses, which “are among the least understood subjects in the scientific world.” He concludes as I had: “The same glass of wine is perceived in different ways by different people” (p.1).
To structure his presentation, Zhu adopts “chemical terroir” and “sensory terroir” as his organizing principles. “The chemical terroir of wine tasting is about the chemical composition of the wine itself that contributes to the sensory profile. Every glass of wine has a unique matrix of chemical components that forms a terroir of its own,” he explains. On the other hand, “The sensorial terroir of wine tasting refers to human perceptions of the chemical compounds in wine” (p.3). Throughout the text, he deftly introduces the appropriate concept or term, though not always defining the latter at first use.
While the intent of the book is clearly pedagogical, Zhu assures us that “as this is not a textbook (and there is no exam) there is no need to have foundational knowledge of chemistry and sensory-related fields” (p.4). While this is true, the subject matter necessarily requires the use of chemical names and other scientific terms that may give the reader pause. The goal is to get on a first-name basis with terms like phenolics, anthocyanins, and terpenoids, while also making accommodation with phenylacetaldehyde, 2-isopropyl-3-methoxypyrazine, and other tongue twisters, but not to pass a PhD-qualifying examination in chemistry or enology. The illustrations lend useful support for the text.
Content from our partners
Chatty, helpful, original
The book is divided into three parts: “Sight,” which contains three chapters; “Palate,” with four chapters; and “Smell,” consisting of five chapters. Each part and chapter follows the advice commonly given to one preparing a lecture: Tell them what you’re going to tell them; tell them; and tell them what you told them. The frequency with which this is done can be viewed as either excessively repetitious or necessarily reinforcing. The epilogue is an opportunity to see how the material presented in the 12 chapters is applied to six wine pairings.
Zhu alludes throughout to research, but because this is not an academic text, he leaves out citations. A list of references by chapter is included for those interested in consulting the primary sources. The extensive index is essential for finding definitions of terms that would be unfamiliar to the tyro taster, especially when they are not given when first introduced.
Since the eyes drink first, sight is addressed at the start. The chapters explain the sources of red, pink, and white color in wine; the impact of color blindness and other differences in color perception in those with normal vision; and other things besides color that we can see in a glass of wine. I, like Zhu, “assumed white wines would be simpler than red wines in terms of chemical composition. But the reality is that white wines are chemically very complex” (p.39). This is one of many factoids I picked up that I will be sharing with visitors to the tasting room.
During the first decade of my involvement with fine wine, I would pay particular attention to the legs that formed on the side of the glass. Naively, I assumed it was an indication of quality, as do some of my guests even now. In a section entitled “Tears—what makes a wine ‘cry’?” Zhu gives a proper explanation of the phenomenon, without mentioning that it is an example of the Gibbs-Marangoni effect, keeping with his approach to minimize technical terminology. He points out that the higher the alcohol and/or the amount of residual sugar, the bigger and thicker the tears, but he makes no mention of them being an indication of quality.
Palate is explored next, with wine’s relationship to each of the five recognized basic tastes: sweet, umami, sour, salty, bitter, and a possible sixth: fat. The last of the four chapters in this part covers tactile sensations and palate changes.
Zhu’s Asian perspective enriches his discussion of umami: “In Japanese, the corresponding kanji character for umami is 旨, which comes from the right half of the character 鮨, and 鮨 is a type of fish and an alternative term for sushi (note the left part of 鮨 is 魚, which means fish). In Chinese, the word for umami is 銶, which consists of 戴 (which again, means fish) and 鸞 (which means lamb)” (p.72).
Given its overwhelming importance in the appreciation of wine, the part devoted to smell occupies the largest number of pages. Zhu tells us: “Theoretically, we can differentiate a trillion different types of smells, even though our vocabulary for naming precise smells is very limited” (p.115). So much, then, for improving the pertinence of tasting notes.
Chapters in this part explore floral and fruity, green, animal, spicy, woody, and petrol smells, as well as oxidation and reduction. A highlight of the book is the description of the production of 2,4,6-trichloroanisole (TCA), the major cause of cork taint. Another is the section “Does wine need to breathe?” Zhu’s chatty style facilitates the understanding of the complex processes without being bogged down with jargon.
I was especially pleased that Zhu does his share in debunking the universal use of “minerality,” which seems to have been mandated in every tasting note for a white wine that aspires to credibility. He notes: “Even many well-trained wine professionals find it almost impossible to provide a good reference for the ‘mineral-like’ smell in wine, because the real minerals on our planet do not contribute to any smell” (p.118).
Again leaning on his Chinese roots, Zhu uses “the yin and yang philosophy to conceptualize oxidation and reduction […] When delving into the study of reduction in chemistry, I envisage the yin elements, embodying counteractive properties like darkness, night, winter, and the moon. On the other hand, when exploring oxidation, I see it as yang, representing proactive attributes such as brightness, day, summer, and the sun” (p.175).
The epilogue invites the reader to conduct a series of tastings to “gain a greater understanding of the chemical and the sensorial terroir of wines” (p.192). Instead of suggesting specific bottles, Zhu wisely recommends types. In his comments on each pair, he refers the reader to the relevant chapters in the book he is reinforcing.
For those whose interest in wine has evolved beyond the simply sip phase, Behind the Glass would be a good first place to look for answers to some fundamental questions. Zhu’s inaugural effort as an author succeeds in sharing a distinctive and friendly view of the science of wine tasting by aligning the discussion along the novel concepts of chemical and sensory terroirs. It is all the more impressive an achievement given that English is Zhu’s second language. He alludes to future editions in which new discoveries can be shared (p.121). This would also be an opportunity to address some of the issues mentioned above. Nevertheless, Zhu has given us another, gentler place to turn for answers when pondering what I am tasting and why.
Behind the Glass: The Chemical & Sensorial Terroir
of Wine Tasting
Gus Zhu MW
Published by Académie du Vin Library; 192 pages (hardback); $25 / £20
